Mobile communication devices, such as cellular telephones, two-way pagers and others typically rely on power from batteries. It is, therefore, advantageous for a mobile communication device to monitor the amount of time remaining before the device loses power due to a drained battery. For example, a mobile communication device may issue a warning signal during a call to avoid an imminent shut-off when the battery output drops below a particular threshold. Typical cellular service provides a three to five minute low-battery warning period during a call and similar warnings when the device is idle.
Mobile communication devices typically measure battery capacity in units of current multiplied by time, such as milliamp hours (mAh). However, direct current measurement may not be available in certain devices. In addition, the variation of battery parameters, such as temperature, equivalent series resistance (ESR), and aging, often make it difficult for a device to perform an accurate prediction. The multi-mode operations available in some devices (e.g., sleep, wake-up, access, traffic) may make this estimation even more difficult.